The '''Harvard College Observatory''' ('''HCO''') is an institution managing a complex of buildings and multiple instruments used for astronomy|astronomical
research by the Harvard University
Department of Astronomy. It is located in Cambridge, Massachusetts|Cambridge
, USA, and was founded in 1839. With the Smithsonian Astrophysical Observatory
, it forms part of the Harvard–Smithsonian Center for Astrophysics
HCO houses a collection of approximately 500,000 Photographic_plate#Astronomy|astronomical plates
taken between the mid-1880s and 1989 (with a gap from 1953–68).
This 100-year coverage is a unique resource for studying temporal variations in the universe. The Digital Access to a Sky Century @ Harvard
project is digitally scanning and archiving these photographic plates.